<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .title {
            color: blue;
        }
        article h1 {
            color: red;
        }
    </style>
</head>
<body>
<article>
    <h1 class="title">我是一级标题</h1>
</article>
<!--// .title 等级是0010-->
<!--// article h1等级是0002-->
<!--// 因此 颜色为blue-->


</body>
</html>